There are many tall tales about contraception and pregnancy - and, if you fall for them, you could be landed with life-changing consequences.

I suspect such myths are responsible for the fact that a third of all UK pregnancies are unplanned.

One in three women asked about the morning-after pill wrongly thought that it wasn't possible to get pregnant if their partner hadn't ejaculated.

The research was carried out on more than 1,000 women who'd had a contraception mishap over the past year and took no action.

Other myths lead to women not choosing some of the most reliable contraception options.

Here are 10 of the most misleading and dangerous ideas that many people believe to be true.

So read on - your future depends on knowing the true facts ...

Myth 1

You can't get pregnant if the man hasn't ejaculated

If you rely on the withdrawal method - where the man removes his penis before he has an orgasm - you have an excellent chance of getting pregnant eventually.

That's because a few sperm could easily be released before orgasm and it only takes one sperm to fertilise an egg. Plus there's a good risk of an accident with this method - no man consistently has that much self-control.

Also, you won't reduce your risk of getting pregnant by douching, showering, bathing or peeing immediately after sex. And the position you have sex in makes no difference.

Myth 2

You can only get pregnant mid-cycle

You're most likely to ovulate (release an egg) between 10 and 16 days before your next period - however, even if you usually have regular periods, factors like stress, age, weight change and medicines can all disrupt the balance of hormones, affecting when this happens. It's even possible to get pregnant during a period.

Also sperm can survive for up to seven days in a woman's body so you could still get pregnant even if you have sex a few days before you ovulate.

Myth 3

You can't get pregnant if you're breastfeeding

The hormones you produce when you're breastfeeding may temporarily prevent ovulation but the extent to which this happens varies, so I'd strongly recommend using contraception as soon as you start having sex again.

Good options for breastfeeding women include the mini Pill, also known as the progestogen-only Pill (POP), which releases hormones to prevent an egg being fertilised or implanted - or the hormone implant, a matchstick-sized rod which releases hormones that prevent ovulation and fertilisation.

Neither contains the hormone oestrogen, which may reduce milk flow.

Myth 4

The morning-after pill has to be used the next day

A better name for this is the emergency contraceptive pill because it can be used up to 72 hours after unprotected sex.

For it to have the best chance of working, you should take it as soon as possible - it's up to 95 per cent effective within the first 24 hours but that reduces to just under 60 per cent by 72 hours.

It' available from your GP's surgery, local NHS genito-urinary medicine clinic, or from pharmacies.

Myth 5

Hormonal contraceptives can reduce fertility

You can get pregnant immediately after stopping the contraceptive Pill or patch, or having an IUS (intrauterine system) or hormone implant removed, no matter how long you've been using them.

With the hormone injection, it may take up to a year for your periods and fertility to return to normal, though there will be no long-term effect on fertility.

The IUS and hormone injection are more than 99 per cent effective, as are the combined Pill and patch, if you follow the instructions.

Myth 6

You need a break from the Pill or patch

The combined Pill and patch work in the same way - by releasing oestrogen and progestogen, preventing ovulation and fertilisation. However, with the patch, which needs to be changed once a week, the hormones are released directly through the skin.

There's no increased risk from using these long-term

providing they were appropriately prescribed.

The combined Pill and patch aren't suitable for smokers who are over 35, or anyone who's very overweight or suffers from several conditions including thrombosis, high blood pressure and diabetes.

Myth 7

The Pill makes you fat

I was involved in research on the combined contraceptive Pill, which showed that women taking it were as likely to lose weight as to gain it.

Any weight you put on is more likely to be due to lifestyle changes, perhaps if you've recently left home. However, if you're prone to premenstrual fluid retention, some pills make this worse, so ask your doctor about changing your brand.

Myth 8

The implant moves around the body

The hormone implant needs to be fitted by a doctor or nurse into the inner area of your upper arm, where it stays put for three years. This takes only about five minutes and is done with a local anaesthetic. It also can't be seen and is more than 99% effective.

Myth 9

Only mums can use an IUS or IUD

You don't have to have had a baby to use either of these devices. The IUD (intrauterine device) is a small, plastic and copper device that's fitted into the womb and can stay put for 10 years.

The copper stops sperm surviving while the device stops a fertilised egg from being implanted in the womb. It may not be suitable if you have heavy periods, an untreated infection or other problems with your womb or cervix.

An IUS is a small plastic device which slowly releases progestogen. This makes it more difficult for the sperm to reach the egg and thins the lining of your womb so an egg can't be implanted if it does get fertilised. Most women who want to use this can do so but speak to your doctor about your options.

Myth 10

Two condoms are safer than one

Wrong! In fact, the friction between the condoms may cause them to tear more easily. If you follow instructions properly, condoms are 95 per cent effective against pregnancy, which isn't as good as the 99 per cent effectiveness of many of the other methods mentioned.

However, they're the only way of protecting yourself from sexually-transmitted infections (STIs) so it's important to use them if you and your partner haven't been tested for STIs.

Visit the FPA (Family Planning association) at www.fpa.org.uk or call its helpline on 0845 122 8690